Prior art discloses forming Grignard reagent in the synthesis of 2,4,5-trifluorobenzoic acid. It is not practical to scale up this reaction to industrial scale.
DeGraw, J. I. et al, Journal of Chemical and Engineering Data, Vol. 13, No. 4, pages 587-588, discloses preparing 2,4,5-trifluorobenzoic acid by hydrogenating nitro-4,5-difluorobenzoic acid (V) in the presence o concentrated hydrochloric acid to form 2-amino-4,5-difluorobenzoic acid hydrochloride (VI), esterifying the carboxyl group by reacting (VI) with methanolic hydrogen chloride, thereby to form methyl 2-amino-4,5-difluorobenzoate hydrochloride (VII), converting VII to methyl 2,4,5-trifluorobenzoate (IX) by forming the diazonium fluoroborate and decomposing in a Schiemann reaction, the hydrolyzing (IX) to form 2,4,5-trifluorobenzoic acid. It has been discovered herein that the route of DeGraw et al can be substantially simplified by starting out with 4,5-difluoroanthranilic acid and converting to the diazonium fluoroborate without an intermediate step of esterifying the carboxyl group. The starting material 4,5-difluoroanthanilic acid is readily prepared, for example, as taught in Fifolt U.S. Pat. No. 4,521,616.